PD-1 is up-regulated on CD8⁺ T cells of CML patients in the chronic phase of the disease. (A) Percentage of PD-1 expression on total CD8⁺ T cells from cpCML patients (●, n = 8) compared with healthy donors (■, n = 8). Horizontal bars indicate the mean. Statistical comparison was made using unpaired 2-tailed Student t test. (B) Correlation between PD-1 expression on total CD8⁺ T cells from cpCML patients and quantitative levels of BCR/ABL:ABL mRNA levels determined by RT-PCR in blood (n = 8). Statistical comparison was made using the Spearman correlation.